The present invention relates generally to angular adjustment of a propulsion nacelle on a tilt-rotor aircraft for reducing drag under flight conditions.
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
During flight of an aircraft, the aerodynamic forces exerted thereon include both lift and drag components. Under cruise flight conditions, lift is produced by aircraft propulsion maintained at a small angle of attack with a certain degree of drag overcome by engine thrust directly related to fuel consumption. On conventional fixed wing aircraft, the nacelles through which propulsion is imparted to the aircraft form part of the aircraft configuration subject to drag during flight under control of movable surfaces on the wings and tail. During aircraft climb, there is an increase in the angle of attack between the air stream and the aircraft fuselage, as well as other aircraft components such as the wings and nacelles, causing an increase in both lift and drag. Such increase in drag results in a costly consumption of energy. It is therefore an important object of the present invention to minimize and/or reduce such increase in drag on the aircraft without excessively costly configurational adjustment of the aircraft.
In accordance with the present invention, pitch orientation control is utilized to provide for angular adjustment of the propulsion nacelles on the fixed wings of a tilt-rotor type aircraft, so as to reduce and minimize drag under flight conditions involving increasing angle of attack between the aircraft and the air stream, without otherwise adversely affecting aircraft operation or requiring costly adjustments. Toward that end, an orientation sensor at the forward end of the aircraft detects angular deviation of the aircraft body from the flow direction of the air stream to generate an error signal is applied through an attitude gyro, to a programmed controller, to which a reference cruise signal input is also applied reflecting a constant angular deviation between the nacelles and the aircraft fuselage. A drive signal output of such controller is fed to an actuator through which the nacelle is angularly adjusted during appropriate flight conditions in accordance with programming of the controller to reduce drag by minimizing the orientation angle between the nacelle centerline and the aircraft body axis.